Presently, a user wishing to interact with a computer system usually does so using a display device such as a computer monitor and an input device such as a keyboard or a computer mouse. Whilst such interfaces are useful, they are relatively bulky and non-portable, and can lack the immediacy and expressiveness afforded by a pen applied to paper. Moreover, in many situations, paper is a more comfortable and convenient recording medium, due to its superior visual characteristics and its portability. Nevertheless, information recorded on paper is generally not as accessible and malleable as information recorded on a computer system. Furthermore, unlike a computer interface, a pen applied to paper generally lacks the ability to control computer software.